Question

What is the percentage composition of hydrogen and oxygen in water?(H=1, O= 16)
A) 11.1, 88.90
B) 12.3, 18.32
C) 15.6, 94.86
D) 34.3, 60.55

Answer 1

As we know that the mass percentage of any element in a compound or a molecule is hundred times the mass of the element which is further divided by the total mass. To calculate the mass percentage of any substance in the compound we can use the following formula:
$\dfrac{Mass Of Element}{mass of compound}\times 100$. We can also find the empirical formula of the compound if we are able to calculate its mass composition.

Complete step by step solution:
The molecular weight of the water is 18g/mol
The mass of hydrogen in water is 2g/mol
So the percentage of hydrogen in water will be calculate by the following formula:
Mass percentage of hydrogen in water= $\dfrac{Mass Of Hydrogen}{mass of water}\times 100$
So now substitute the values in the formula then we get,
Mass percentage of hydrogen in water= $\dfrac{2g/mol}{18g/mol}\times 100=11.11$
The mass of oxygen in water is 16g/mol
The molecular weight of water is 18g/mol
So the formula for calculating the mass percentage of oxygen in water will be:
Mass percentage of oxygen in water=$\dfrac{mass of oxygen}{mass of water}\times 100$
Mass percentage of oxygen in water=$\dfrac{16}{18}\times 100=88.90$

Hence,the correct option is C.

Note: So if one has found the mass percentage of the element in the compound then we can find the empirical formula of that compound too. The empirical formula is the simplest whole number ratio of each type of the atom in the compound. It can be the same as that of the compound formula but not always. To convert it to empirical formula the steps are that firstly get the mass of each element of the compound in grams. Then find their respective number of moles. Then divide each element number of moles by the smallest number of moles. Then convert them to whole numbers and put those numbers as the subscript in the empirical formula.